1. Field of the Invention
The invention relates to a method and a device for drying and keeping dry especially rolled strip (cold-rolled strip) up to approximately 10 mm thickness, preferably smaller than 0.2 mm thickness, in the delivery area of cold rolling and strip-rolling plants, wherein, for separating the xe2x80x9cdamp areaxe2x80x9d of the rolling mill relative to the further delivery area, xe2x80x9cdry areaxe2x80x9d, downstream of the last roll stand, a partition is arranged whose upper part extends above the strip up to the stand platform and whose lower part below the strip extends down to the base plate.
2. Description of the Related Art
In the delivery area of rolling mills the required quality of the product xe2x80x9ccold-rolled stripxe2x80x9d, in addition to good flatness and optimal thickness tolerance, includes also dryness and cleanness of the strip surface because otherwise surface errors, for example, stains, are unavoidable during further processing of the strip.
In order to obtain a dry strip surface and to shield it relative to the damp area of the rolling mill and to protect it in this way from becoming wet again, for example, by undesirable condensation of the vapors which are emitted by the rolling stand, different devices and measures are known, such as, for example, partitions, removal by vacuum, removal by blowing as well as combinations thereof.
Accordingly, in DE 28 44 434 A1 it is suggested to remove by vacuum liquid residue from sheet metal and strips continuously transported through particularly rolling mills and strip treatment plants in a defined area transverse across the sheet metal surface by means of vacuum generated with suction tubes, that is, by means of the vacuum flows produced thereby. The suction tubes provided with a longitudinal slot have attached laterally thereto sealing lips of rubber, plastic, or brushes which laterally seal the suction area relative to the strip.
From DE 44 22 422 A1 a device for a contactless sealing of a gap between a partition and a working roll in the delivery area of a roll stand is known. The end of the partition is positioned contactless with a minimal gap-shaped spacing substantially tangentially at the surface of the working roll. The gap which is formed in this way between the partition and the working roll is sealed by an energy-rich flow (in the form of compressed air) exiting from a gap nozzle arranged in the end area of the partition. The underpressure, which is produced in this way by the flow as a result of the cutting edge-like tapered configuration of the end portion and its arrangement relative to the working roll, has the effect that additionally larger amounts of air are taken through the gap and flow in the direction toward the damp area of the working roll. This provides a defined flow between partition and the rolling stock, and the wet air with droplets and other particles is removed by suction within the flow area.
A further type of partition for keeping dry cold-rolled strip in the delivery area of a roll stand by deflecting means for deflecting liquid rolling medium and/or for removing sprayed or splashed liquid adhering to surfaces of the strip is described in DE 195 35 168 A1. The partition, comprised of a fixedly installed part and a movable part arranged at the strip side (for making possible a problem-free exchange of the rolls), extends above the strip delivery area up to the stand platform and below the strip delivery area down to the base plate. On the movable part of the partition the following device parts are arranged:
a roll barrel blowing device for removing squeezed-off rolling medium from the finish-rolled strip;
a roll barrel gap seal for sealing the roll space located above the strip relative to the strip;
a strip edge blowing device for generating an air flow at a right angle to the strip in the roll gap at the delivery side above the running strip by which the entrained rolling oil is deflected away from the strip laterally of the strip edge;
a vapor suction device configured to generate a parallel air flow counter to the strip running direction above and below the strip.
Based on this known prior art, wherein in many cases the strip is subjected to a vacuum action or an air flow is directed against the working roll, the object of the invention is to configure a simple method and a device, based on this method and comprised of simple components which are suitable for rolling mills, for a contactless sealing of a gap between a partition and a strip at the delivery area of cold-rolling and strip rolling devices such that, with an acceptable energy expenditure and a minimal noise development, a dry strip surface as well as a complete separation of the damp-wet roll area from the finish-rolled strip are achieved by developing the known devices further.
The object is solved according to the invention in regard to a method of the aforementioned kind in that the strip is subjected, by the ends of the partition facing the strip and its components, to a gas under pressure, preferably air, at a right angle to the strip surface from above and from below via blast nozzles, so that across the entire strip width an air cushion-like compressed gas buffer is generated in the gap between the ends of the partition facing the strip and the upper and lower strip surfaces, the gap having a width of 0.1 to 1 mm, preferably 0.2 mm, and the compressed gas is guided away above and below the strip parallel to the strip surface in the form of a split flow in the direction toward the rolling mill or the damp area and of a split flow in the opposite direction toward the dry area, and in regard to the device by blast nozzle bars arranged at the end of the movable partitions facing the strip across the entire strip width having blast nozzles oriented perpendicularly onto the strip surface and blast nozzle surfaces formed facing the strip and extending parallel to the strip surface.
By means of the measure of the invention of sealing the gap between the partition and the strip above and below the strip by an air cushion-like compressed gas buffer, wherein the compressed gas above and below the strip is removed additionally in the form of a split flow parallel to the strip surface in the direction toward the rolling mill and in the opposite direction, even at high strip speeds of more than 1,000 m per minute, independent of the strip width, a penetration of rolling oil or emulsion is prevented successfully and a contactless strip drying is achieved.
By means of the generated split flow extending parallel to the strip surface, it is furthermore safely prevented that rolling oil or emulsion can penetrate laterally past the strip. Also, liquid that is running downwardly on the upper partition is returned in a directed manner to the rolling mill by this split flow.
The pressure with which the gas is guided at a right angle from above and below against the strip surface is approximately 1 to 10 bar, preferably approximately 5 bar, which ensures that the generation of an air cushion-like compressed gas buffer required for an optimal sealing action is realized and that the subsequent split flow is energy-rich enough in order to prevent penetration of moisture. In order to make this possible with an energy amount and noise development as minimal as possible, the gap between the partition and the strip is, if possible, adjusted to 0.1 to 1 mm, preferably to 0.2 mm, the strip thickness being added to this, in order to achieve the desired effect for a predetermined gas pressure with gas quantities as minimal as possible.
A device for performing this method is comprised of a partition arranged above and below the strip whose stationary installed parts are positioned above the strip so as to extend up to the stand platform and below the strip down to the base plate. In the direction facing the strip, these fixedly installed partition components are extended by movable (slidable) partition components so far that between these movable partition components and the strip surface a narrow gap is adjusted. This gap can be adjusted by moving the movable partition components against a stationary or adjustable stop to realize a predetermined gap width, or it is adjusted automatically as a result of the compressed gas buffer. According to a preferred embodiment of the invention, the gap is, independent of the strip thickness, 0.1 to 1 mm, preferably 0.2 mm.
The end of the movable partition facing the strip is formed by a blast nozzle bar, respectively, in which bores (blast nozzles) are arranged through which a gas is guided under pressure against the strip surface. According to another advantageous embodiment of the invention, approximately 250 blast nozzles, per meter of bar length, with a diameter of approximately 1 mm are arranged in the blast nozzle bar. Advantageously, the blast nozzles are arranged successively transverse across the entire strip width centrally within the blast nozzle bar. However, it is also possible to provide, instead of the blast nozzle bores, a continuous slot nozzle in the blast nozzle bar having a slot width of, for example, 1 mm.
As a result of the size of the blast nozzle barxe2x80x94its length corresponds at least to the strip width and its width is approximately 10 to 500 mm, preferably approximately 60 mmxe2x80x94as well as of the blast nozzle bar surface formed parallel to the strip surface at the side facing the strip, the compressed gas which centrally exits (relative to the width of the blast nozzle bar) from the blast nozzles is able to build up the required air cushion-like compressed gas buffer for a reliable sealing action. Moreover, as a result of the wide configuration of the blast nozzle bar surface at the side facing the strip, whose width projects considerably past the area of the blast nozzle openings and which extends parallel to the strip surface, it is achieved that the gap to be sealed is wide enough in the direction of the strip length in order to maintain, by means of the compressed gas, a reliably acting split flow parallel to the strip surface in the direction toward the rolling mill and in the opposite direction.